There have so far been proposed a wide variety of apparatuses each of which comprises an intermediate shaft of a vehicular drive shaft, and a dynamic damper having a bending vibration damping function for a measure against gear noise and booming noise. However, the intermediate shaft of the drive shaft is generally a steel rod or a rotation shaft with no damping ability, thereby resulting in such problems as a so-called rattling noise, jerkiness and the like caused by torsion vibrations of a drive system. Here, the rattling noise is generated with idling gear pairs in a transmission clashing with each other by torsional resonances of the drive system while a vehicle is accelerated or decelerated in middle and high speed gears.
On the other hand, as a vehicular damping mechanism for damping the torsion vibrations of the drive system, there has so far been known a damper disc type of damping mechanism constructed to have first and second stage properties. The first stage property is to generate hysteresis relatively small with a first resilient member and a first friction generation mechanism at the time of a relative torsion angle of an input portion to an output portion being small, while the second stage property is to generate hysteresis relatively large with a second resilient member larger in spring pressure than the first resilient member and a second friction generation mechanism capable of producing a larger friction than the first friction generation mechanism.
The known damper disc type of vibration damping mechanism comprises a first friction generation mechanism having an urging member curved in a radial direction and in a shape of disc spring, and a hub moving mechanism for moving a flange in an axial direction away from a first disc plate when the relative torsion angle between the flange serving as input and output members and the first disc plate exceeds a predetermined angle. When the hub moving mechanism is operated, the engagement position (fulcrum position in a radial direction) of the urging member curved in cross section to the second plate connected to the first plate across the flange is gradually displaced. The displaced engagement position causes the hysteresis torque generated by the friction of the urging member and the flange to be radially increased steplessly, thereby making it possible to smoothly vary the torsion property at the time of the first and second stage properties being switched over between them (see for example Patent Document 1).
However, the damper disc type of vibration damping mechanism thus constructed leads to its large dimension in the radial direction, so that the damping mechanism is likely to be subject to the limitation in layout. It is therefore not suitable to mount the damper disc type of vibration damping mechanism on the intermediate shaft of the drive shaft.
In view of this problem, there has so far been proposed another vibration damping mechanism provided in a hollow hole formed in a power transmission shaft to make the vibration damping mechanism not to be subject to the limitation in layout.
The known vibration damping mechanism has a first shaft formed with a hollow hole, and a second shaft having one end portion fixed to the inner circumferential portion of the first shaft and the other end portion spaced apart from the inner circumferential portion of the first shaft to form an annular gap therebetween having an annular friction member filled therein. The friction member functions to generate a hysteresis torque in response to the relative torsion between the first and the second shafts. The magnitude of the hysteresis torque is set to be proportionate to the torsion rigidity of the second shaft and the torsion angle between the input and output end portions of the first shaft (see for example Patent Document 2).
Patent Documents
    Patent Document 1: Patent Publication No. H9 (1997)-100874    Patent Document 2: Patent Publication No. 2006-038138